A key concept of the program project is that periventricular leukomalacia (PVL) results from ischemia/reperfusion that triggers free radical injury to vulnerable developing oligodendrocytes in perinatal white matter: as a result, developing oligodendrocytes die, in part by apoptosis, thus resulting in decreased mature oligodendrocytes and impaired myelination. The overall hypothesis of the proposed study is two-fold: 1) there is a specific vulnerability of developing oligodendrocytes to oxidative stress in the cerebral white matter in the period of greatest risk for PVL (24-32 weeks) which relates, at least in part, to a mismatch between the development of the expression of antioxidant enzymes and the development of pro-oxidant pathways, such as the acquisition of iron necessary for oligodendrocyte differentiation; and 2) oxidative stress plays a major role in the pathogenesis of PVL. In baseline studies, we will determine the temporospatial maturation of oligodendrocytes in human cerebral white matter using immunocytochemical methods and markers to stage-specific oligodendrocytes. We will also determine the developmental profile of selected antioxidant enzymes and markers of pro-oxidant pathways (i.e., iron, nitric oxide synthase localization, and 12-lipoxygenase expression) in human cerebral white matter using histochemistry, immunocytochemistry, and immunoblotting. Here we will test the hypothesis that antioxidant enzymes are expressed at low levels in immature white matter during the period of greatest risk for PVL, and that the appearance of markers of pro-oxidant pathways precede the expression of antioxidant enzymes, thus denoting a developmental mismatch between potential sources of free radicals and the systems to clear them. In PVL itself, we will determine the densities of developing oligodendrocytes, indicative of a targeted death and loss of these cells. We will also determine if markers of oxidative stress are expressed in PVL. Finally, we will determine the involvement of selected cytokines in PVL. The proposed studies should provide important insight into the roles of developing oligodendrocytes and factors related to oxidative stress in PVL directly within the human brain.